The invention relates to a locking device with a detent element axially displaceable by means of an electromechanical drive from an unlocking position into a locking position, and vice versa.
Locking devices of this type are known and are used, above all, for the electric locking of the steering spindle of a steering apparatus of a motor vehicle. Thus, for example, EP 0 764 566 A1 discloses a locking device which comprises an electric motor arranged in a housing, with a following spindle drive for displacing a detent element from its locking position into its unlocking position, and vice versa, the detent element, in its locking position, engaging into the recess, formed by adjacent teeth, of a toothed ring fastened to the steering spindle and consequently blocking the steering spindle.
One disadvantage of this known device, inter alia, is that, in the event of a mechanical defect in the drive train (for example, if the spindle is broken off, etc.) or in the event of pronounced vibrations of the locking device, the situation where the detent element is displaced into its locking position, even during travel, is not ruled out.
German patent application DE 199 06 268 A1 already discloses a locking device, in which the detent element is provided laterally with a recess, into which, for fixing it in the unlocking position, a securing element designed as a lever is pivoted by means of a prestressed spring. In this case, the securing element is pivotable about an axis arranged parallel to the longitudinal axis of the spindle drive. For the securing element to be pivoted out, there is a shaft activated by the drive part of the threaded spindle via a control cam. In practice, however, the use of a securing element of this type activated by the threaded spindle presents problems when the drive is a drive without limit stops (drive with freewheel), such as is known, for example, from DE 199 61 975 C1, because, in this case, the control contour, together with the drive part, is displaced in terms of its axial position.
The object in which the invention is based is to specify a compactly constructed locking device with a securing element which is pivotable or displaceable for fixing the detent element and which can be actuated in a simple way into its detaining position or into its releasing position even when the drive used for displacing the detent element is a drive with freewheel.
This object is achieved, according to the invention, by means of the features of claim 1. Further particularly advantageous refinements of the invention are disclosed in the subclaims.
The invention is based essentially on the notion, on the one hand, of providing a control contour on the axially displaceable drive part, but, on the other hand, of selecting the distance between the control cam and the securing element in such a way that, with the detent element in the unlocking position, the control cam is displaced axially in relation to the control contour and is consequently located outside the range of action of the control contour. When the electromechanical drive is activated in order to displace the detent element into its locking position, the securing element initially remains in its detaining position. The detent element or the driver is thereby supported on the securing element, and the drive part together with the control contour is displaced axially, counter to the pressure of a compression spring, in the direction of the control cam, until the control cam comes into engagement with the control contour. By means of the control contour then acting on the control cam, the cam and consequently also the securing element are actuated, and the detent element or the driver is released, so that the prestressed spring abruptly displaces into the locking position the arrangement consisting of the drive part, driver and detent element.
Insofar (when a freewheel is used) the securing element changes its position only when the arrangement consisting of the drive part, driver and detent element is moved completely in the locking and unlocking directions, a detection of both end positions of the arrangement can be carried out by means of only one sensor by the position of the securing element being interrogated.
The control contour may have a ramp-shaped design in the axial direction, in such a way that, as a result of the axial displacement of the drive part, the control cam executes its pivoting movement necessary for releasing the securing element. However, as a rule, this presupposes a relatively large axial stroke movement of the drive part. In order to keep this stroke movement smaller, it has proved advantageous to design the control contour of the drive part in such a way that, during the upwardly directed displacement of the drive part, the control cam is supported on a helical outwardly directed contact surface on the control contour.
The securing element may be designed both as a pivotable lever and as a linearly guided bolt, the connection between the respective securing element and the control cam being capable of being made in various ways.